The benzotriazoles have long been an important class of UV absorbers and have gained wide commercial importance and acceptance for many industrial applications. The prior art is replete with references to their manufacture and utility. However, as requirements become ever more stringent and demanding, the search for still more stable and durable benzotriazoles continues. The gradual phase out of HAPS solvents, such as xylene, because of environmental concerns and their replacement with non-HAPS solvents, such as esters, ethers or ketones, and increased durability requirements for automotive coatings make this search more urgent. Indeed, the automotive industry is most concerned about UVA losses from automotive paints and coatings as seen in the publication by J. L. Gerlock et al., Proc. 36th Annual Tech. Sym. (Cleveland Coating Society), May 18, 1993.
U.S. Pat. Nos. 4,226,763; 4,278,589; 4,315,848; 4,275,004; 4,347,180; 5,554,760; 5,563,242; 5,574,166 and 5,607,987 describe selected benzotriazoles, substituted in the 3-position of the hydroxyphenyl ring by an α-cumyl group, which show very good durability in automotive coatings. These benzotriazoles represent the present state of the art. The instant invention is directed at preparing benzotriazoles which exhibit still better durability and low loss rates from the prior art benzotriazoles.
U.S. Pat. Nos. 5,278,314; 5,280,124; 5,436,349 and 5,516,914 describe red-shifted benzotriazoles. These benzotriazoles are substituted in the 3-position of the phenyl ring with an α-cumyl group and at the 5-position of the benzo ring by thio ethers, alkylsulfonyl or phenylsulfonyl moieties. Red-shifting the benzotriazoles is desirable for spectral reasons. A group at the 5-position which is also electron withdrawing provides additional benefits in low loss rates and durability as found in the instant invention. Missing from these patents are any alkylsulfones with seven or fewer carbon atoms. When such sulfonyl substituents are combined with specifically α-cumyl moieties, extremely durable compounds result which, due to the bulk of the α-cumyl moiety have sufficiently low volatility to be useful in coating and other polymer systems.
The presence of an α-cumyl or phenyl group ortho to the hydroxy group on the phenyl ring exerts a surprisingly large positive effect on benzotriazole photo stability in coatings and photographic gel systems. The magnitude of this effect, particularly when compared to a tert-butyl group in that position, is well beyond prediction. The combination of both an electron withdrawing group on the benzo ring and an α-cumyl or phenyl group on the phenyl ring in the same molecule leads to extremely desirable properties in coating systems when high UV absorber permanence is critical.
Novel compounds meeting these parameters as being extremely stable in aggressive use environments constitute a first portion of this invention.
The presence of the electron withdrawing moiety at the 5-position of the benzo ring has a powerful stabilizing effect on benzotriazoles in general and is observed in other polymer systems such as polycarbonate and poly(vinyl chloride) substrates as well. However, the effect of having an α-cumyl or phenyl group ortho to the hydroxy moiety on the phenyl ring is much smaller to non-existent in some polymer systems such as polycarbonate or poly(vinyl chloride) even though critical for coating systems as described above.
In addition to being more photostable, the compounds of this invention are red-shifted, absorbing strongly in the 350–400 nm wavelength range. While such red-shifting is desirable in that a greater portion of the UV spectrum is absorbed, this can also introduce color if the absorption beyond 400 nm is significant. This can limit the use of such compounds, particularly in systems such as polycarbonate glazing applications or present difficulties in various pigmented systems.
It is found that the nature of the substituent ortho to the hydroxyl group on the phenyl ring has an unexpected impact on color imparted to the substrate by the benzotriazole. Thus, relatively subtle differences in substitution on the phenyl ring can have a large impact on the resulting color and the applicability of the benzotriazole in specific color sensitive applications. There are striking differences between having hydrogen, alkyl or α-cumyl at this 3-position.
Furthermore, U.S. Pat. No. 5,977,219 teaches that, when the 5-position of the benzo ring is substituted with a trifluoromethyl group, the resulting benzotriazole not only exhibits the same or greater enhanced stability when incorporated into thermoplastic resins, but also imparts less color than related benzotriazoles substituted at the 5-position with other electron withdrawing moieties such as sulfonyl or carbonyl. These trifluoromethyl compounds also absorb strongly in the 350–400 nm wavelength range despite the low color and are extremely compatible in a wide range of substrates such as acrylic resins, hydrocarbons, polycarbonates and poly(vinyl chloride).
There are a multitude of general references to benzotriazoles having in the 5-position of the benzo ring electron withdrawing groups such as esters, amides, sulfones and the like that are not substituted in the 3-position of the phenyl ring by an α-cumyl or phenyl moiety. In many of these references the broadly described compounds are unexemplified and no teaching or appreciation taught of the positive effect on photostability described in this invention. In any event, the vast majority of these structures fall well outside the scope of instant invention.
Japanese 1996-299547 discloses the use of heterocyclic compounds as non-aqueous electrolytes for lithium batteries. These heterocyclic compounds included benzotriazoles substituted on the benzo ring by hydrogen, methyl, ethyl, amino, hydroxyl, 2-pyridyl or phenyl; and substituted on the hydroxyphenyl ring by at the 5-position by a methyl group and at the 3-position by hydrogen, methyl, ethyl, amino, hydroxyl, 2-pyridyl or phenyl.
U.S. Pat. No. 4,396,712 describes generically benzotriazole compounds which are substituted at the 5-position of the benzo ring by phenyl as light stabilizers for photothermographic film. The only compound disclosed specifically is 5-phenyl-2-(2-hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole. The benzotriazole UV absorbers provide improved storage stability by stabilizing the silver salts (oxidizing agents) in these dry image forming materials. Only selected low molecular weight benzotriazoles are suitable since the benzotriazole must be compatible with other components of the image forming materials.
A. Suzuki, Pure & Applied Chem., 66, No. 2, 213 (1994) describes a new synthetic method involving the reaction of sterically hindered aryl boronic acids or esters with sterically hindered haloarenes in the presence of palladium (II) catalysts. This reaction has become known as the Suzuki reaction.
B. E. Huff et al., Organic Synthesis, 75, 53 (1998) describe the synthesis of unsymmetrical biaryls using a modified Suzuki cross-coupling to form 4-biphenylcarbox-aldehyde.
J. P. Wolfe, et al., J. Am. Chem. Soc., 1999, 121, 9550 describe the use of highly active palladium catalysts for Suzuki coupling reactions.
WO 00/22037 describes the stabilization of solid, shaped and colored wax articles using a malonate UV absorber which may be substituted by a hindered amine group.
Japanese Hei 5-93164 discloses the use of benzotriazole UV absorbers and hindered amines in stabilizing pigmented wax crayons.
Copending U.S. patent applications Ser. Nos. 09/496,084; 09/495,495 and 09/495,496 all describe the stabilization of candle wax using other types of benzotriazole UV absorbers.